Mobile communications devices such as cellular phones, personal digital assistants (PDA), or so-called smart phones have become commonplace. Applications and service offerings beyond those related to conventional calling, e-mail, and Internet access have increased rapidly in recent years. A specific area of significant development has been location-based services, by which information or functions are provided to the mobile communications device depending on its geographical location.
Navigation services typically involve the mobile communications device displaying a location of the mobile communications device on a map. Users can also request a route from a desired starting location, such as a present location or user supplied location, to a desired destination. Turn-by-turn directions can be provided in textual, visual (e.g., map), or audible format in real-time while the device travels along the route.
For providing navigational services, map applications on mobile communications devices can access either onboard maps or parts of offboard maps. Onboard maps are comprehensive maps stored locally on the mobile communications device, beyond any snippets of maps stored in a cache (e.g., RAM) of the device. Onboard maps cover an area, such as a state, country, or continent. Onboard maps covering even a relatively small region, such as a large city and its metropolitan area, require a relatively large amount of data for mobile communications devices to store. For example, a current comprehensive map of the United States can require up to 2 or 3 GB of memory, taking up to ten, twenty or even twenty-five percent of the storage capacity of some devices. Because of this, onboard maps are most commonly used with dedicated navigation devices. Another shortcoming of using onboard maps is that they become more and more out-of-date with time, requiring regular and sometimes-large or time-consuming updating downloads.
Offboard maps are stored remote to the mobile communications device by a map service. A portion of the map is downloaded to the mobile communications device as needed, such as in response to a request by the user for routing to a desired destination. The amount of map data downloaded is much less than the amount of data stored for onboard systems. And because the downloaded map data is only needed for the task at hand (e.g., routing to a present destination), the data does not need to be kept on the device after the task is completed. Another benefit of offboard maps is that the most up-to-date map data is available for the user because the map service regularly updates the remotely-stored maps that are downloaded to the device when needed.
A drawback of using offboard maps is dependence on coverage and bandwidth of the wireless communications network. If a user moves into an area lacking coverage or sufficient available bandwidth, additional map data cannot be sent to the device over the network.